Process for preparing cooagulants for water treatment

ABSTRACT

This invention relates to a process for preparing proteins that can act as effective coagulants in the treatment and purification of contaminated water. In particular, the invention relates to a process for extracting coagulant protein derivatives from the seeds of trees from the family Moringaceae. The invention also relates to coagulation protein preparations prepared by the process, and the use of such preparations for the treatment and purification of contaminated water.

[0001] The present invention relates to a process for preparing proteinsthat can act as effective primary coagulants in the treatment andpurification of contaminated water. In particular it relates to aprocess for extracting coagulant protein derivatives from seeds of treeswithin the family Moringaceae and especially those of Moringa oleiferaLam (syns Moringa pterygosperma Gaertn.).

[0002] The seeds of Moringa oleifera Lam (hereinafter referred to asMoringa) are utilised primarily to obtain an edible oil, which isextracted using a mechanical press. The residue from this extractionprocess is known as presscake. It has been found that the seeds ofMoringa oleifera contain water soluble, low molecular weight, highlybasic proteins that can act as primary coagulants in contaminated watertreatment. The crushed/powdered seed suspensions and presscake, whichremains following oil extraction, have been found to be effectivecoagulants but they suffer from the disadvantage that they result in alarge amount of residual insoluble material which requires disposing of.

[0003] The object of the present invention is to provide an extractionprocess which results in the maximum yield of coagulation proteins fromMoringa seeds. The extraction process should preferably be suitable foruse in less developed countries thereby providing inexpensive coagulantproteins for water treatment.

[0004] According to one aspect of the invention there is provided aprocess for preparing coagulation proteins from Moringa seeds whichcomprises the steps of:

[0005] 1. treating Moringa seed presscake and/or whole seed inclusive ofshell to produce an evenly divided granular powder having for example aparticle size of from 0.5 to 2.5 mm diameter; and

[0006] 2. adding the granular powder to a complex salt solution,preferably an aqueous solution containing chlorides of calcium(typically 0.5-1.5 g/l), magnesium (typically 3.0-5.0 g/l), potassium(typically 0.5-1.0 g/l) and sodium (typically 20-30 g/l), in order toleach protein out of the powder; and

[0007] 3. separating the protein solution from the remaining solids; and

[0008] 4. precipitating certain organic compounds including proteins,enzymes and carbohydrates, by heating the solution; and

[0009] 5. removing the precipitates from solution and removing excesswater to concentrate the product protein preferably in the form of asuspension of solids.

[0010] The process preferably comprises the additional step of dryingthe protein slurry to a moisture content of 15% or less, preferably 10%or less, most preferably 5% or less.

[0011] The extraction process is a series of unit operations, each setup to perform an essential step in the extraction of proteins and theirconversion into a state for practical use from the seeds of the Moringaoleifera Lam tree.

[0012] The process will be further described with reference to theaccompanying figures in which:

[0013]FIG. 1 is a schematic drawing of the first part of the process;and

[0014]FIG. 2 is a schematic drawing of the second part of the process.

[0015] The unit operations of the process are taken in sequence.

[0016] Size Reduction

[0017] The presscake is received as an unevenly sized, randomlyagglomerated granular material.

[0018] This operation consists of a feed hopper (1) from which thepresscake is fed at a controlled rate into a mill (2) the designprinciples of which are suitable for the presscake.

[0019] On leaving the mill the presscake has been converted to an evenlydivided granular powder of a particle size typically 0.5-2.5 mmdiameter, preferably 1-2 mm diameter, and with a minimum of very fineparticles which would reduce the efficiency of a later separationoperation.

[0020] The milled product is collected in a receiving hopper (3)incorporating an exhaust duct for the airflow induced by the mill. Thereceiving hopper has a device such as a rotary valve to facilitatedischarge of the product into containers or onto a conveyor (4) fortransport to the extraction operations.

[0021] Extraction

[0022] This consists of one or more process vessels (5) and a facility(7) for providing a complex salt solution, i.e. typically an aqueoussolution containing chlorides of calcium (1 g/l), magnesium (4 g/l),potassium (0.75 g/l) and sodium (24 g/l).

[0023] The process vessel is typically a vertical cylindrical tank witha base sloping to a discharge outlet and equipped with a mixer (6)employing a propeller or dispersion type rotating agitator.

[0024] In operation, the vessel is filled with the complex salt solutionand the granular powder is added in a specified proportion, typically20% w/w and thoroughly dispersed.

[0025] It is then continuously agitated under ambient temperatureconditions for a period of time sufficient for the complex salt solutionto leach the protein out of the dispersed powder. Whilst the period oftime may be varied to suit the nature of the powder, approximately 1hour has been found effective.

[0026] At the completion of the leaching operation, the contents of thevessel are in the form of a slurry with spent presscake solids suspendedin the solution of complex salt and extracts.

[0027] The slurry is transferred using a positive displacement pump (8)to a decanting centrifuge or a filter press, and most effectively thelatter, to separate the solution from the spent powder solids. The spentpowder has a moisture content in the range of, for example, 15-30%. Therecovered solution is collected in holding vessels (10).

[0028] Separation of Proteins

[0029] From holding vessels (10) the solution of complex salt andextracts is transferred by pump (11) to a system of heat exchangers (12)in which its temperature is raised above 70° C. and typically to 95° C.for a period of between 0.5 and 1 minute. Sufficient agitation, eitherthrough hydraulic or mechanical means, is provided to ensureprecipitated material does not get burnt onto the container surface. Themain section of the heat exchangers may use steam as an indirect heatingmedium with a suitable temperature control system for the solution.Optimum energy efficiency is achieved in the primary section of the heatexchangers by using the outgoing hot solution to indirectly heat theingoing cold solution.

[0030] During the operation of raising the temperature of the solutionabove 70° C. certain organic compounds (including proteins, enzymes andcarbohydrates) are precipitated to form a solid suspension in thesolution. These materials are a byproduct and the suspension isdischarged from the heat exchangers through a separator (13), typicallya centrifuge used for continuous operation of disk-stack design. Theprecipitated materials are collected as a dense slurry or cake and theclarified solution is discharged directly from the centrifuge underpressure to holding vessels (14).

[0031] Concentration

[0032] From holding vessels (14) the solution is fed to an operation inwhich excess water is removed. This may take the form of a multistagevacuum evaporator or preferably a selective membrane filter commonlyknown as an ultrafilter (15). The latter method is used when considereddesirable to remove low molecular weight solutes from the solution inaddition to water and is undertaken using a membrane typically ofnominal pore size 5,000 Kilo Daltons and a differential pressuretypically of 20 psi. The whole operation typically makes a 10 foldincrease in the concentration of the product protein. The concentratedproduct is discharged in the form of a suspension of solids in asaturated solution which is transferred into holding vessels (16).

[0033] The concentrated product held in vessels (16) may be packed anddistributed for direct use (as a flocculating agent). Alternatively, itmay be dehydrated in a drying operation fed by a pump (17) from thevessels (16).

[0034] Drying

[0035] If the process is conveniently located, the protein in the stateof a thick slurry is available for immediate use (as a water treatmentaid). However, it must be assumed that in the form of a large scaleefficient factory it will be remote from the various points of use ofthe protein. For this major purpose, the state of the protein is changedto that of a dry powder in which it is resistant to degradation and isconvenient for storage, transport and use.

[0036] This operation includes a system for drying the thick slurry to amoisture content preferably 15% or less and producing the protein in afinely divided form for convenience of use.

[0037] Freeze drying is a method which dries the protein to a friablesolid which breaks up to a fine granular state. The preferred method isspray-drying which dries the protein without unwanted degradation andsimultaneously converts it to a fine powder.

[0038] The spray dryer (18) consists of a chamber into which the slurryis fed at a controlled rate by a positive displacement variable capacitypump (17). The slurry is dispersed in the chamber in the form of verysmall droplets by means of an atomiser nozzle or atomiser rotating disk.A large volume of air is simultaneously introduced which has been heatedto a temperature typically of 200° C. The method achieves a rapid rateof evaporation of the water component of the slurry without raising theproduct temperature to a damaging level and for this protein thedischarge temperature is limited to 100° C. or less, preferably a rangeof 80°-90°, most preferably a range of 84-87° C.

[0039] The final product is discharged at two available locations (20)from the spray drying system via a rotary valve or similar method fromwhich it is filled directly into containers for transport or into aconveyor system for transfer to a filling process.

[0040] In use, the liquid concentrate is typically diluted 2:1 in cleanwater and an applied at doses of 1-20 mg/l (equivalent protein content)for portable water treatment depending on the nature of the water to betreated. For wastewater applications the dose range will be between 5and 50 mg/l (equivalent protein content).

[0041] The dry product is prepared as a 5% (w/v) stock solution in cleanwater and dosed at similar amounts, based on equivalent protein content,as the liquid concentrate depending on application.

1. A process for preparing coagulant proteins from seeds of trees of thefamily Moringaceae which process comprises the steps of: treating seedpresscake and/or whole seed to produce and evenly divided granularpowder; adding the granular powder to a salt solution comprisingchlorides of calcium, magnesium, potassium and sodium to leach proteinout of the powder; separating the protein solution from the remainingsolids; precipitating certain organic compounds by heating the solution;and removing the precipitates from solution and removing excess water toconcentrate the product protein.
 2. A process according to claim 1 whichcomprises the additional step of drying the protein slurry to a moisturecontent of 15% or less.
 3. A process according to claims 1 or 2, whereinthe seeds are derived from Moringa oleifera Lam.
 4. A process accordingto any one of claims 1 to 3, wherein the granular powder has a particlesize from 0.5 to 2.5 mm diameter.
 5. A process according to claim 4,wherein the granular powder has a particle size of from 1 to 2 mmdiameter.
 6. A process according to any one of claims 1 to 5, whereinthe salt solution comprises an aqueous solution containing chlorides ofcalcium (0.5-1.5 g/l), magnesium (3.0-5.0 g/l), potassium (0.5-1.0 g/l)and sodium (20-30 g/l).
 7. A process according to any one of claims 1 to6, wherein the temperature of the solution of complex salt and extractsis raised above 70° C.
 8. A process according to any one of claims 1 to7, wherein the protein solution and precipitated materials are separatedby centrifuging.
 9. A process according to any one of claims 1 to 8,wherein the protein solution is concentrated by filtration.
 10. Aprocess according to any one of claims 1 to 9, wherein the proteinsolution is spray dried.
 11. A process according to any one of claims 1to 9, wherein the protein solution is freeze dried.
 12. A coagulationprotein preparation suitable for use in the purification of water whenprepared according to any one of the processes of claims 1 to
 11. 13.Use of a protein preparation according to claim 12, for the treatmentand purification of contaminated water.